The invention relates to a circuit arrangement for igniting and operating a lamp, comprising
supply terminals for connection to a supply voltage source, PA1 a piezotransformer equipped with two input terminals and two output terminals, PA1 an oscillator, coupled with the supply terminals and the input terminals of the piezotransformer, for generating a periodical voltage, PA1 a load circuit equipped with terminals for lamp connection and coupled between the output terminals of the piezotransformer.
Such a circuit arrangement is known from EP 0665600. The piezotransformer is only very small, so that the known circuit arrangement is very suitable for use in for instance a flat panel display. In the known circuit arrangement both the ignition voltage as well as the voltage present over the lamp during stationary operation are both generated by the piezotransformer. In practice this means that the circuit arrangement can only be used in combination with lamps that have a relatively low ingnition voltage while a relatively high voltage is present over the lamp during stationary operation. The possible applications of the known circuit arrangement are therefore limited. In practice only low pressure discharge lamps can be ignited and operated by means of the known circuit arrangement. High pressure discharge lamps, however, are characterized by a very high ignition voltage while the voltage that is present over the lamp during stationary operation is relatively low. Circuit arrangements for igniting and operating high pressure discharge lamps are typically equipped with either a series- or a parallel igniter for generating an ignition pulse with a relatively high voltage. These igniters tend to be bulky, increasing the size and the cost of the circuit arrangement In case of a series igniter the igniter is arranged in series with the lamp, so that at least part of the series igniter carries a current not only during ignition but also after ignition of the lamp during stationary operation, which leads to power dissipation and therefore a relatively low efficiency of the circuit arrangement. On the other hand, in case use is made of a parallel igniter (arranged in parallel with the lamp), part of the circuit arrangement needs to be protected against the ignition pulse by means of a filter. This filter, however, not only functions during ignition but also carries a current during stationary operation and therefore decreases the efficiency of the circuit arrangement.